SAN FRANCISCO— A new report demonstrating a 26 percent gap between the most and least fuel-efficient airlines serving America’s domestic market shows the Environmental Protection Agency is missing an opportunity to make huge cuts to aviation greenhouse gas pollution. A federal judge ruled nearly three years ago that the EPA must address aviation’s fast-growing carbon emissions, but the agency still has not acted.

Alaska Airlines and Spirit were the most fuel-efficient carriers in the report released today by the International Council on Clean Transportation thanks to their use of advanced aircraft technology and efficient practices. American Airlines and Allegiant were the least efficient, according to the council’s ranking of the 13 largest mainline domestic carriers operating in the United States. Dramatic aviation emission reductions are easily achievable, the report shows, despite the airline industry’s claim that fuel costs already force them to operate as efficiently as possible.

“This report knocks the legs out from under the Obama administration’s excuses for not regulating the aviation industry’s massive and growing greenhouse gas pollution,” said Vera Pardee, a senior attorney with the Center for Biological Diversity’s Climate Law Institute. “The EPA needs to stop dragging its feet and start setting rules that push inefficient airlines to curb their damaging emissions. We’ve got to hold polluters accountable for disrupting our climate.”

The Center and other environmental organizations filed a lawsuit in 2010 to force the EPA to set aviation greenhouse gas pollution standards. A federal judge quickly ruled that the EPA must address aircraft emissions under the Clean Air Act. But after nearly three years, the agency has still not finished the first step in its rulemaking process.

Aviation accounts for about 11 percent of carbon dioxide emissions from the U.S. transportation sector and is one of the fastest-growing sources of carbon pollution, rising 3 percent to 5 percent a year. Carbon emissions from global aviation will quadruple by mid-century without action.

“The airlines keep telling us that the EPA should ignore their carbon pollution because they’re already doing everything possible to reduce it,” Pardee said. “But a 26 percent gap between the most and least efficient U.S. airlines proves that is simply not true.”

The Center for Biological Diversity is a national, nonprofit conservation organization with more than 775,000 members and online activists dedicated to the protection of endangered species and wild places.